Formation of 6-n-pentyl-2H-pyran-2-one (6-PAP) and other volatiles by different Trichoderma species

Seventy-seven headspace Trichoderma isolates belonging to eight species— T . atroviride , T . citrinoviride , T . hamatum , T . harzianum , T . koningii , T . viride , T . viridescens , and T . virens —were screened for their ability to produce 6-n-pentyl-2H-pyran-2-one (6-PAP) and other volatiles using solid phase microextraction (SPME) coupled to gas chromatography–mass spectrometry (GC-MS). Intra- and interspecies variability was demonstrated in the 6-PAP synthesis. The most efficient producer of 6-PAP on potato dextrose agar (PDA) was T . atroviride . However, the variation in 6-PAP synthesis differed significantly among strains of this species, the lowest value being 33.4 μg (strain AN212), whereas the highest reached 1,426 μg per culture for strain AN35. Also, T . viridescens produced significant amounts of 6-PAP (200.1–526.3 μg for 11 out of 12 strains). Moderate producers were isolates belonging to T . hamatum (up to 155 μg) and T . citrinoviride (up to 200 μg). Trichoderma viride isolates showed very little production of 6-PP on PDA. No 6-PAP formation was detected in cultures of 25 isolates belonging to three species, T . koningii , T . harzianum , and T . virens . Trichoderma atroviride AN35, as the most efficient producer of 6-PAP, was selected to observe the dynamics of 6-PAP formation during growth on PDA at 20 °C for 6 days. A radical increase in 6-PAP production started after the fourth day of incubation, and the maximum expression was achieved in the final phase of the experiments, 6 days after inoculation. Apart from 6-PAP, over 40 other volatile compounds were detected in the survey of Trichoderma species. Among them, the most commonly produced substrates were 1-octene-3-ol, isoamyl alcohol, 3-octanone, cyclohept-3-en-1-one, 2-pentylfuran, linalol isobutyrate, toluene, D-limonene, and α-bergamotene. Seventeen of the detected compounds have never previously been reported as a secondary metabolite of Trichoderma .